The effects of levcromakalim and pinacidil on the human internal mammary artery

Effect of Type-2 Diabetes Mellitus on the Expression and Function of Smooth Muscle ATP-Sensitive Potassium Channels in Human Internal Mammary Artery Grafts

Here we have shown for the first time altered expression of the vascular smooth muscle (VSM) KATP channel subunits in segments of the human internal mammary artery (HIMA) in patients with type-2 diabetes mellitus (T2DM). Functional properties of vascular KATP channels in the presence of T2DM, and the interaction between its subunits and endogenous ligands known to relax this vessel, were tested using the potassium (K) channels opener, pinacidil. HIMA is the most commonly used vascular graft in cardiac surgery. Previously it was shown that pinacidil relaxes HIMA segments through interaction with KATP (SUR2B/Kir6.1) vascular channels, but it is unknown whether pinacidil sensitivity is changed in the presence of T2DM, considering diabetes-induced vascular complications commonly seen in patients undergoing coronary artery bypass graft surgery (CABG). KATP subunits were detected in HIMA segments using Western blot and immunohistochemistry analyses. An organ bath system was used to interrogate endothelium-independent vasorelaxation caused by pinacidil. In pharmacological experiments, pinacidil was able to relax HIMA from patients with T2DM, with sensitivity comparable to our previous results. All three KATP subunits (SUR2B, Kir6.1 and Kir6.2) were observed in HIMA from patients with and without T2DM. There were no differences in the expression of the SUR2B subunit. The expression of the Kir6.1 subunit was lower in HIMA from T2DM patients. In the same group, the expression of the Kir6.2 subunit was higher. Therefore, KATP channels might not be the only method of pinacidil-induced dilatation of T2DM HIMA. T2DM may decrease the level of Kir6.1, a dominant subunit in VSM of HIMA, altering the interaction between pinacidil and those channels.

The vascular effect of glibenclamide: A systematic review

Objective:

To systematically review the vascular effects of glibenclamide.

Background:

Infusion of adenosine triphosphate (ATP)-sensitive potassium (KATP) channel opener (KCO) levcromakalim dilates cranial arteries and induces headache and migraine attacks. Recent data show that levcromakalim-induced vasodilation is associated with headache. Glibenclamide is a KATP channel blocker that may alter the vascular tone and thus has an impact on headache or migraine prevention.

Methods:

A search through PubMed was undertaken for studies investigating the vascular effects of glibenclamide in vitro as well as in vivo published until July 2019.

Results:

We identified 58 articles; 31 in vitro studies, 24 in vivo studies and 3 studies with both. The main findings were that glibenclamide inhibited levcromakalim-induced and other KCOs-induced vasodilation, while the basal vascular tone remained unchanged.

Conclusion:

Glibenclamide could inhibit vasodilation by KCOs, and further studies are needed to clarify the vascular effect of glibenclamide on human cranial arteries.

Different potassium channels are involved in relaxation of rat renal artery induced by P1075

The ATP-sensitive K(+) channels opener (K(ATP)CO), P1075 [N-cyano-N'-(1,1-dimethylpropyl)-N″-3-pyridylguanidine], has been shown to cause relaxation of various isolated animal and human blood vessels by opening of vascular smooth muscle ATP-sensitive K(+) (K(ATP)) channels. In addition to the well-known effect on the opening of K(ATP) channels, it has been reported that vasorelaxation induced by some of the K(ATP)COs includes some other K(+) channel subtypes. Given that there is still no information on other types of K(+) channels possibly involved in the mechanism of relaxation induced by P1075, this study was designed to examine the effects of P1075 on the rat renal artery with endothelium and with denuded endothelium and to define the contribution of different K(+) channel subtypes in the P1075 action on this blood vessel. Our results show that P1075 induced a concentration-dependent relaxation of rat renal artery rings pre-contracted by phenylephrine. Glibenclamide, a selective K(ATP) channels inhibitor, partly antagonized the relaxation of rat renal artery induced by P1075. Tetraethylammonium (TEA), a non-selective inhibitor of Ca(2+)-activated K(+) channels, as well as iberiotoxin, a most selective blocker of large-conductance Ca(2+) -activated K(+) (BK(Ca)) channels, did not abolish the effect of P1075 on rat renal artery. In contrast, a non-selective blocker of voltage-gated K(+) (K(V)) channels, 4-aminopyridine (4-AP), as well as margatoxin, a potent inhibitor of K(V)1.3 channels, caused partial inhibition of the P1075-induced relaxation of rat renal artery. In addition, in this study, P1075 relaxed contractions induced by 20 mM K(+) , but had no effect on contractions induced by 80 mM K(+). Our results showed that P1075 induced strong endothelium-independent relaxation of rat renal artery. It seems that K(ATP), 4-AP- and margatoxin-sensitive K(+) channels located in vascular smooth muscle mediated the relaxation of rat renal artery induced by P1075.

A role of ion channels in the endothelium-independent relaxation of rat mesenteric artery induced by resveratrol

Recently it has been suggested that resveratrol relaxes different isolated arteries. The present study addressed the question whether different ion channels are involved in the endothelium-independent mechanism of vasodilatation induced by resveratrol. For that purpose, we tested the action of resveratrol on the rat mesenteric artery without endothelium. Resveratrol induced concentration-dependent relaxation of rat mesenteric artery. Among the K(+)-channel blockers, 4-amynopiridine (4-AP) moderately antagonized the resveratrol-induced relaxation, while glibenclamide, tetraethylammonium chloride, charybdotoxin, margatoxin, and barium chloride did not inhibit resveratrol-induced vasorelaxation. In rings, precontracted with 100 mM K(+), the relaxant responses to resveratrol were highly significantly shifted to the right compared to those obtained in rings precontracted with phenylephrine, but resveratrol-induced maximal relaxation was only slightly affected. In order to minimize the influence of K(+) channels and voltage-gated Ca(2+) channels (VGCCs) in vascular smooth muscle, the third contraction was made by 100 mM K(+) in the presence of nifedipine. The relaxant response to resveratrol was abolished. Thus, the mechanism of vasorelaxation induced by resveratrol probably involves activation of 4-AP-sensitive K(+) channels. Its ability to completely relax the mesenteric artery precontracted with K(+)-rich solution suggests that K(+) channel-independent mechanism(s) are involved in its vasorelaxant effect. It seems that interaction with VGCCs plays a part in this K(+) channel-independent effect of resveratrol.

The effect of potassium channel opener pinacidil on the non-pregnant rat uterus

The effects of the K(+) channel opener, pinacidil on the spontaneous rhythmic contractions and contractions provoked by electrical field stimulation (50 Hz) or by oxytocin were investigated in the isolated uterus of the non-pregnant rat in oestrus. Pinacidil produced more potent inhibition of oxytocin-elicited contractions than of spontaneous rhythmic contractions or electrical field stimulation-induced contractions. Glibenclamide, a selective blocker of adenosine triphosphate (ATP)-sensitive K(+) (K(ATP)) channels, antagonized the pinacidil-induced inhibition of contractions elicited by oxytocin in a competitive manner. However, the pinacidil-induced inhibition of electrical field stimulation-elicited contractions and spontaneous rhythmic contractions was antagonized non-competitively by glibenclamide. In the uterine strips pre-contracted with 80 mM K(+), the pinacidil-induced maximal relaxation was not affected. The present data show that pinacidil exhibits potent relaxant properties in the rat non-pregnant uterus in oestrus and therefore should be taken into account as a possible agent for treatment of dysmenorrhoea. Based on glibenclamide affinity, it appears that the inhibitory response to pinacidil involves K(ATP )channels. We need further investigations to explain why the interaction between glibenclamide and pinacidil in this experimental model depends on the nature of contractions. The ability of pinacidil to completely relax the rat non-pregnant uterus pre-contracted with K(+)-rich solution suggests that K(+) channel-independent mechanism(s) also play a part in its relaxant effect.

Potassium channel opener pinacidil induces relaxation of the isolated human radial artery

Taking into consideration that the search for drugs capable of modifying blood flow through human radial artery (RA) is warranted, the present study was designed to examine the vasodilatatory effects of the potassium channel opener, pinacidil on the RA and to define the contribution of different K+ -channel subtypes in the endothelium-independent pinacidil action on this blood vessel. Pinacidil relaxed the RA rings with endothelium and without endothelium with comparable potency. N-nitro-L-arginine methyl ester (L-NAME) and methylene blue did not affect the pinacidil-induced vasorelaxation in rings with endothelium. In the rings without endothelium, the K+ -channel blockers glibenclamide and tetraethylammonium (TEA) moderately antagonized the pinacidil-induced relaxation, while charybdotoxin and 4-aminopiridine did not. In endothelium-denuded rings, precontracted with 100 mM K+, the relaxant responses to pinacidil were highly significantly shifted to the right compared to those obtained in RA precontracted with phenylephrine, but pinacidil-induced maximal relaxation was not affected. Addition of nifedipine did not but addition of nifedipine and nickel (Na+ -Ca2+ exchanger inhibitor) did cause a statistically significant rightward shift of the pinacidil concentration-relaxation curve, although the effect 0.1 mM pinacidil was preserved. Thus, pinacidil induces relaxation of the human RA in endothelium-independent manner, and glibenclamide- and TEA-sensitive vascular smooth muscle K+ channels are probably involved. Its ability to completely relax the RA precontracted with K+ -rich solution suggests that pinacidil has additional K+ channel-independent mechanism(s) of action. It seems that stimulation of the forward mode of the Na+ -Ca2+ exchanger plays a part in this K+ channel-independent effect of pinacidil.

Potassium Channels-Mediated Vasorelaxation of Rat Aorta Induced by Resveratrol

Resveratrol, a phenolic substance present in grapes and a variety of medical plants, has been reported to induce vasorelaxation, however the mechanisms are uncertain. In this paper we investigate the possible participation of K(+) channels in the endothelium-independent vasodilatation of rat aorta induced by resveratrol. Resveratrol induced concentration-dependent relaxation of rings with endothelium and without endothelium. We used different potassium channel inhibitors to determine whether the K(+) channels mediated endothelium-independent relaxation of rat aorta induced by resveratrol. Highly selective blocker of ATP-sensitive K(+) channels, glibenclamide, as well as non-selective blockers of K(+) channels, tetraethylammonium, did not block resveratrol-induced relaxation of rat aortic rings. Charybdotoxin, a blocker of calcium-sensitive K(+) channels did not affect the resveratrol-induced relaxation. 4-Aminopiridine, non-selective blocker of voltage-gated K(+) (Kv) channels, and margatoxin that inhibits Kv1 channels abolished relaxation of rat aortic rings induced by resveratrol. In conclusion, we have shown that resveratrol potently relaxed rat aortic rings with denuded endothelium. It seems that 4-aminopiridine and margatoxin-sensitive K(+) channels located in the smooth muscle of rat aorta mediated this relaxation.

Effect of the oral hypoglycaemic sulphonylurea glibenclamide, a blocker of ATP-sensitive potassium channels, on walking distance in patients with intermittent claudication

AIMS

The oral hypoglycaemic sulphonylurea glibenclamide stimulates endogenous insulin secretion through blockade of ATP-sensitive potassium (KATP) channels on pancreatic beta cells, but also blocks cardiovascular KATP channels, leading to increased peripheral vascular resistance and reduced peripheral blood flow in non-diabetic subjects. Therefore, this study examined whether a single oral dose of glibenclamide adversely affected the pain-free or maximal walking distance in patients with intermittent claudication.

METHODS

In a double-blind, randomized crossover study, 12 non-diabetic patients with intermittent claudication were given a single oral dose of glibenclamide (5.25 mg) or placebo separated by a washout period of 1 week. A treadmill test was carried out 180 min after glibenclamide/placebo intake for determination of pain-free and maximal walking distance. Plasma glucose concentrations were kept constant by an euglycemic clamp. Changes in ankle/brachial blood pressure index (ABI), serum insulin, and serum glibenclamide were also assessed.

RESULTS

The pain-free walking distance was 62.8 +/- 9.8 metres (mean +/- sem) after glibenclamide and 52.6 +/- 5.9 metres after placebo (P = 0.52). The maximal walking distance was 142.7 +/- 18.7 metres after glibenclamide and 132.6 +/- 16.6 metres after placebo (P = 0.23). The ABI was not significantly changed by glibenclamide compared with placebo. Serum glibenclamide was 0.51 +/- 0.08 microm 180 min after administration of the drug. Glibenclamide produced an 8-fold increase in circulating insulin compared with placebo (P < 0.001).

CONCLUSIONS

Glibenclamide given as a single oral dose commonly used in glucose-lowering drug therapy does not reduce pain-free or maximal walking distance in non-diabetic patients with intermittent claudication.

Analysis of Vasoreactivity of Isolated Human Radial Artery

Radial artery (RA) is increasingly used as graft for coronary artery bypass grafting due to its good long-term patency. However, the mechanism of peri- and post-operative spasm is still unclear. Because of that, the aim of our study is to analyze the contractility of RA and to determine whether the presence of functional endothelium alters its contractile properties. Contractions of isolated RA rings were provoked by exogenously applied vasoconstrictors or by electrical field stimulation (EFS, 20 Hz). The order of vasoconstrictors potency based on their EC50 values was as follows: angiotensin II > phenylephrine > 5-hydroxytriptamine. Presence of endothelium increased both EC50 and maximal contraction to phenylephrine and angiotensin II, but inhibited reactivity of RA to 5-hydroxytriptamine. Spontaneous rhythmic contractions (SRC, <4 mHz) and EFS-induced contractions of RA are endothelium-independent and weaker than contractions induced by exogenously applied vasoconstrictors. Our study concludes that RA shows marked sensitivity and reactivity to angiotensin II, phenylephrine, and 5-hydroxytriptamine. Further investigations are necessary to answer why angiotensin II and phenylepehrine induce stronger contractions in the presence of endothelium. In addition, SRC as well as contractions of neurogenic origin may take part in developing vascular spasm of RA.

The Mechanism of Endothelium-Independent Relaxation Induced by the Wine Polyphenol Resveratrol in Human Internal Mammary Artery

Resveratrol, a stilbene polyphenol found in grapes and red wine, produces vasorelaxation in both endothelium-dependent and endothelium-independent manners. The mechanisms by which resveratrol causes vasodilatation are uncertain. The aim of this study was to investigate the mechanism(s) of endothelium-independent resveratrol-induced vasorelaxation in human internal mammary artery (HIMA) obtained from male patients undergoing coronary artery bypass surgery and to clarify the contribution of different K+ channel subtypes in resveratrol action in this blood vessel. HIMA rings without endothelium were precontracted with phenylephrine. Resveratrol induced a concentration-dependent relaxation of the HIMA. A highly selective blocker of ATP-sensitive K+ channels, glibenclamide, as well as nonselective blockers of Ca2+-sensitive K+ channels, tetraethylammonium and charybdotoxin, did not block resveratrol induced relaxation of HIMA rings. 4-Aminopyridine (4-AP), non selective blocker of voltage gated K+ (KV) channels, and margatoxin that inhibits KV1.2, KV1.3, and KV1.6 channels abolished relaxation of HIMA rings induced by resveratrol. In conclusion, we have shown that resveratrol potently relaxed HIMA rings with denuded endothelium. It seems that 4-AP- and margatoxin-sensitive K+ channels located in smooth muscle of HIMA mediated this relaxation.

pH effects on high conductance Ca2+-activated K+ channels (BKCa) in human internal mammary artery smooth muscle cells

INTRODUCTION

In vascular smooth muscle cells, different types of K+ channels participate in the regulation of membrane potential and consequently in the contractile behavior of the vessel. There is little information about the properties and role of K+ channels in human internal mammary artery (HIMA), the vessel of choice for coronary revascularization.

METHODS

Patch-clamp technique on isolated HIMA smooth muscle cells was used.

RESULTS

This work presents for the first time single-channel properties of the high conductance Ca2+-activated K+ channel (BK(Ca)) of HIMA. It presents a single-channel conductance of 228+/-4 pS (n=44, 8 cells), is sensitive to 100 nM iberiotoxin, and its open probability is Ca2+- and voltage-dependent. Inside-out results show that BK(Ca) channels in HIMA are directly activated by increasing the pH of intracellular media (NPo=0.096+/-0.032 at pH 7.4 and NPo=0.459+/-0.111 at pH 7.6, n=12 cells, p<0.05) and inhibited by lowering this pH (NPo=0.175+/-0.067 at pH 7.4 and NPo=0.051+/-0.019 at pH 6.8, n=13 cells, p<0.05).

CONCLUSIONS

The evidences presented about single-channel properties and intracellular pH sensitivity of BK(Ca) from HIMA smooth muscle cells provide useful information to elucidate physiological or pathological mechanisms in this vessel, as well as for future studies where drugs could have BK(Ca) channels as targets for pharmacological therapies.

Differential antivasoconstrictor effects of levcromakalim and rilmakalim on the isolated human mammary artery and saphenous vein

It is well established that spasm of an arterial and venous graft conduit may occur during harvesting or after coronary artery bypass grafting (CABG). The antivasoconstrictor effect of levcromakalim and rilmakalim, K(+) channel openers (KCOs), was studied in isolated human internal mammary artery (HIMA) and human saphenous vein (HSV) prepared for CABG. HIMA and HSV rings were contracted by electrical field stimulation (EFS, 20 Hz ) or with exogenous noradrenaline (NA). Levcromakalim induced a concentration-dependent and equipotent inhibition of contraction of HIMA and HSV preconstricted by EFS and exogenoulsy applied NA, while rilmakalim produced a stronger inhibition of EFS- than NA-evoked contractions. Glibenclamide, a selective ATP-sensitive K(+) channel (K(ATP) channel) blocker, significantly antagonized levcromakalim-induced inhibition of EFS- and NA-evoked contractions, as well as rilmakalim-induced inhibiton of EFS-evoked contractions on HIMA and HSV. However, glibenclamide failed to antagonize rilmakalim-induced inhibition of NA-evoked contractions. The results suggest that the antivasoconstrictor effect of levcromakalim occurs postsynapticaly by the opening K(ATP) channels in the vascular smooth muscle cells. They also suggest that the effect of rilmakalim on EFS-evoked contractions involves K(ATP) channels located pre-synaptically. However, the mechanism by which rilmakalim inhibits NA-evoked contraction seems to be K(ATP) channel independent and warrants further elucidation.

Contractile responses of the human umbilical artery to KCl and serotonin in Ca-free medium and the effects of levcromakalim

It is known that K(ATP) channel openers inhibit the release and refilling of Ca(2+) from intracellular stores. The present study was designed to test the effects of levcromakalim in human umbilical artery (HUA) rings stimulated by serotonin (5-HT) and KCl in Ca-free medium. Umbilical cords were obtained at vaginal or cesarean deliveries from healthy, term pregnancies. After the isolation, HUA rings were placed in organ baths in solution with indomethacin (10(-5) M) and N(G)-nitro-L-arginine methyl ester (L-NAME) (10(-3) M) at 37 degrees C and aerated with 95% O(2) and 5% CO(2) for the measurement of isometric force. In Ca-free solution with Ethylene glycol-bis (ss-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) (2 mM) the contractions produced by 5-HT (10(-6) M) and KCl (40 mM) decreased significantly. Afterwards, HUA rings were treated with 5-HT and KCl in repeated manner in Ca-free medium. In contrast to KCl, 5-HT induced contractions reduced in each application, progressively. Levcromakalim (10(-4) M) abolished the contractions elicited by 5-HT. On the other hand, levcromakalim had a little but significant inhibitory effect on KCl induced contraction in Ca-free medium. These results suggest that Ca(2+) is not the only transduction pathway in KCl produced contractions of HUA smooth muscle cells.

Contribution of Na+ -Ca2+ exchanger to pinacidil-induced relaxation in the rat mesenteric artery

1 Pinacidil relaxes blood vessels through opening the K(ATP) channels with a resultant membrane hyperpolarization and inhibition of Ca(2+) influx. The aim of this study was to examine the mechanisms thereby pinacidil induces K(+) channel-independent relaxation in isolated endothelium-denuded rat mesenteric artery. 2 Pinacidil-induced relaxation was inhibited by glibenclamide (1-10 micro M) in phenylephrine-preconstricted rings, but was unaffected by glibenclamide after inhibition of K(+) channels and VGCCs. Pinacidil-induced K(+) channel-independent relaxation remained unchanged after treatment with cyclopiazonic acid (10 micro M), thapsigargin (1 micro M), ouabain (100 micro M), propranolol (10 micro M), Rp-cAMPS triethylamine (30 micro M), L-NNA (100 micro M), or ODQ (10 micro M). 3 Pinacidil induced more relaxant effect in the presence of nifedipine than in the presence of 60 mM K(+) plus nifedipine. Pretreatment with Na(+)-Ca(2+) exchanger inhibitors, nickel (30-300 micro M) or benzamil (20 micro M) attenuated pinacidil-induced relaxation in normal or in nifedipine-containing solution. Pinacidil (1 micro M) produced less relaxant effect with decreasing extracellular Na(+) concentration. Na(+)-free condition abolished the inhibitory effect of benzamil. Both nickel and benzamil inhibited pinacidil-induced relaxation in the presence of glibenclamide (10 micro M). Nickel (300 micro M) did not affect the relaxant response to sodium nitroprusside. 4 Pinacidil relaxed the rings preconstricted by active phorbol and U46619 with similar potency. 5 The present results indicate that stimulation of the forward mode Na(+)-Ca(2+) exchange pathway is in part responsible for pinacidil-induced K(+) channel-independent vasorelaxation. Pinacidil also induces K(+) channel-dependent but VGCCs-independent relaxation. The PKC-mediated cellular pathway may be a target site for pinacidil only in higher concentrations.

Differential effects of pinacidil and levcromakalim on the contractions elicited electrically or by noradrenaline in the portal vein of the rabbit

The present study was undertaken to examine the antivasoconstrictor effects of pinacidil and levcromakalim, two potassium channel openers (PCOs), on the isolated rabbit portal vein and to define the role for different subtypes of pre- and/or post-synaptic K+ channels in the antivasoconstrictor action of the PCOs. The vein strips were contracted by electrical field stimulation (EFS) or by exogenous noradrenaline (NA). The results of this study showed that pinacidil produced a more potent inhibition of the neurogenic contractions (pD2 = 6.04 +/- 0.05) than of contractions induced by exogenous NA (pD2 = 4.90 +/- 0.10). Glibenclamide (1 microM), a selective blocker of adenosine triphosphate (ATP)-sensitive K+ channels (K(ATP)), did not affect the pinacidil-induced inhibition of contractions evoked by exogenous NA. In contrast, glibenclamide (0.1-10 microM) significantly antagonized the effect of pinacidil on EFS evoked contractions in a noncompetitive manner. There was no difference between the inhibitory effects of levcromakalim on neurogenic contractions (pD2 = 7.58 +/- 0.05) and contractions evoked by exogenous NA (pD2 = 7.64 +/- 0.08). Glibenclamide (1 microM) antagonized in the same manner the levcromakalim-induced inhibition of neurogenic contractions and contractions evoked by exogenous NA. Moreover, glibenclamide competitively antagonized the effect of levcromakalim on EFS induced contractions of the rabbit portal vein (pA2 = 6.40 +/- 0.10). Charybdotoxin (0.4 microM) and apamin (0.1 microM) did not influence the inhibitory effects of pinacidil and levcromakalim, both on contractions evoked by EFS and contractions evoked by exogenous NA. These results suggest that the antivasoconstrictor effect of levcromakalim might be postsynaptic and associated with opening of the smooth muscle K(ATP) channels. In contrast, it is hypothesized that the effect of pinacidil on neurogenic contractions is due to an interference with K(ATP) channels in the neuromuscular synapse. It seems that the action of pinacidil on the NA contractions is mediated by another still undefined mechanisms of pinacidil.